Authors: EYÜP SOPACI, ATİLLA ARDA ÖZACAR
Abstract: The 30 October 2020 Samos earthquake (Mw = 7.0) ruptured a north-dipping offshore normal fault north of the Samos Island with an extensional mechanism. Aftershocks mainly occurred at the western and eastern ends of the rupture plane in agreement with the Coulomb static stress changes. Mechanism of aftershocks located west of the rupture supported activation of the neighboring strike-slip fault almost instantly. In addition, a seismic cluster including events with Mw~4 has emerged two days later at the SE side of Samos Island. This off-plane cluster displays a clear example of delayed seismic triggering at nearby active faults. In this study, numerical simulations are conducted to mimic the instant and delayed seismic triggering observed after this event and evaluate resultant seismic cycle perturbations at adjacent faults and near İzmir, where amplified ground motions caused heavy damage. For this purpose, Coulomb static stress changes and seismic waveforms recorded by strong-motion stations are combined as static and dynamic triggers on a rate-and-state friction dependent quasi-dynamic spring slider model with shear-normal stress coupling. According to our results, earthquakes with Mw ≤ 3.5 can be triggered instantly, and Mw ≥ 4 events noticeably advance in failure time. However, instant triggering occurs only when static stress loading is very high, and the fault is close to fail, explaining the delayed triggering observed SE of Samos Island. Simulations also revealed that the shear-normal stress coupling increases static loading but does not affect the dynamically controlled failure time advances observed at the end of the seismic cycle. After the earthquake, some of the faults adjacent to the rupture are more likely to fail, especially the long strike-slip fault segment capable of generating large earthquakes at the western edge. On the other hand, the Samos earthquake induced no significant dynamic triggering on far away faults near İzmir.
Keywords: Earthquake triggering, failure time advance, rate-and-state friction, quasi-dynamic
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